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Carotid sheath:Glossopharyngeal
The glossopharyngeal nerve is the ninth (IX) of the twelve pairs of cranial nerves. It exits the brainstem out from the sides of the upper medulla and through the jugular foramen. It has somatic sensory, general and special sensory, and motor. Origin: * Glossopharyngeal nuclei are in upper & middle medulla ** Motor fibers to stylopharyngeus muscle originate innucleus ambiguus ** Sensory fibers pass from superior and inferior ganglia of the nerve to the spinal nucleus of CN5. This supplies tympanic membrane, soft palate, tongue base & pharynx terminate in spinal nucleus CN5 ** Taste fibers from posterior 1/3 tongue terminate in solitary tract nucleus ** Parasympathetic fibers to parotid gland originate in inferior salivatory nucleus Cisternal Segment * Exits lateral medulla in postolivary sulcus just above vagus nerve * Travel anterolaterally through basal cistern together with vagus nerve & bulbar portion of accessory nerve * Passes through glossopharyngeal meatus into pars nervosa Skull Base Segment * Passes through anterior pars nervosa portion of jugular foramen ** medial to the inferior petrosal sinus ** Vagus (CN10) & spinal accessory (CN11) nerves are posterior within pars vascularis portion of jugular foramen ** Superior & inferior sensory ganglia of CN9 are found within jugular foramen *** superior ganglion (jugular ganglion): situated in the upper part of the groove in which the nerve is lodged during its passage through the jugular foramen; it is very small, and is usually regarded as a detached portion of the petrous ganglion *** inferior ganglion (petrous ganglion): larger than the superior and is situated in a depression in the lower border of the petrous portion of the temporal bone Extracranial Segment * Exits jugular foramen into anterior carotid space * Passes lateral to internal carotid artery and deep to stylopharyngeus muscle * Curves forward, forming an arch on the side of the neck and lying on the middle pharyngeal constrictor muscle * Terminates in posterior sublingual space in floor of mouth (posterior 1/3 taste function) and is finally distributed to the palatine tonsil, the mucous membrane of the fauces and base of the tongue, and the mucous glands of the mouth. Extracranial Branches * tympanic nerve (nerve of Jacobson): the tympanic nerve exits the jugular foramen and passes by the inferior glossopharyngeal ganglion; it re-enters the skull through the inferior tympanic canaliculus and reaches the tympanic cavity where it forms a plexus (the tympanic plexus) in the middle ear cavity; the nerve travels from this plexus through a canal and out into the middle cranial fossa adjacent to the exit of the greater petrosal nerve; here the nerve becomes the lesser petrosal nerve; the lesser petrosal nerve exits the cranium via the foramen oval and synapses in the otic ganglion * muscular branch: distributed to the stylopharyngeus muscle * carotid branches: (superior caroticotympanic n. and inferior caroticotympanic n.) descend along the trunk of the internal carotid artery as far as its origin, communicating with the pharyngeal branch of the vagus, and with branches of the sympathetic nerves * pharyngeal branches: are three or four filaments which unite, opposite the middle pharyngeal constrictor with the pharyngeal branches of the vagus and sympathetic nerves, to form the pharyngeal plexus: branches from this plexus perforate the muscular coat of the pharynx and supply its muscles and mucous membrane * tonsillar branches: supply the palatine tonsil, forming around it a plexus from which filaments are distributed to the soft palate and fauces, where they communicate with the palatine nerves * lingual branches: are two in number; one supplies the vallate papillae and the mucous membrane covering the base of the tongue; the other supplies the mucous membrane and follicular glands of the posterior part of the tongue, and communicates with the lingual nerve * sinus nerve, or "Hering's nerve": the branch of the glossopharyngeal nerve to the carotid sinus is the nerve that runs downwards anterior to the internal carotid artery communicates with the vagus and sympathetic then divides in the angle of bifurcation of the common carotid artery to supply the carotid body and carotid sinus; it carries impulses from the baroreceptors in the carotid sinus (to help maintain a more consistent blood pressure) and from chemoreceptors in the carotid body Supply There are a number of functions of the glossopharyngeal nerve: * receives general sensory fibers from the tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue * receives special sensory fibers (taste) from the posterior one-third of the tongue * receives visceral sensory fibers from the carotid bodies * supplies parasympathetic fibres to the parotid gland via the otic ganglion * supplies motor fibres to stylopharyngeus muscle, the only motor component of this cranial nerve * contributes to the pharyngeal plexus